In order to accelerate the changing of the pipette tips, the magazine is not permanently connected to the pipetting device, but rather forms an integral unit with the pipette tips. This integral unit is detachable from the pipette device and, therefore, can be changed together with all of the pipette tips.
The magazines are rectangular plates with holes arranged in a grid and have, independently of the number of holes and, thus, the number of pipette tips that the holes can accommodate over the length and width of the plates, identical device-specific outer dimensions.
An important factor for ensuring the precision of the volume of fluid to be aspirated or dispensed through the pipetting channels is, inter alia, the hermetic seal between the sleeves and the pipette tips, which at present is solved by two different engineering principles.
In the case of the cone principle, which has been widely accepted for the manually operated single channel pipette and duplicated, the upper end of the pipette tips sits on or in cones formed on the sleeves. These cones hold the pipette tips in a force-locking manner and seal relative to the sleeves. This principle is associated with a plethora of drawbacks predominantly because of the inaccuracy of the pipette tips induced by the injection molding technology. A few examples that can be mentioned here include the uncertain simultaneous sealing of all of the pipette tips and the enormous upward lifting forces.
In order to avoid these drawbacks, a sealing principle, in which the ends of the sleeves that face the pipette tips extend into an elastic sealing plate, has established itself in parallel to the cone principle. In this case the pipette tips, with each tip enclosing one end of a sleeve, are sealed off from the sleeves indirectly by means of the sealing plate. For this purpose the pipette tips have a tip shoulder, from which the tips are suspended in a magazine and which presses the tips against the sealing plate.
The elastic sealing plate can be eliminated, if special pipette tips, which are made of two different synthetic plastic materials, are used. In the case of the pipette tips the actual tip body for aspirating reagents is made, like conventional pipette tips made of a synthetic plastic material, of polypropylene. In contrast, the tip shoulder is made of a thermoplastic elastomer, so that the pipette tips can be sealed off directly from the sleeves.
Since it is irrelevant for the description of a pipetting device according to the invention whether the pipette tips are sealed off indirectly by means of a sealing plate or directly by means of an elastic tip shoulder, the description below is based on a conventional sealing method by means of a sealing plate for the sake of simplicity.
In order to ensure a reliable seal, the magazine, in which the pipette tips are suspended from their tip shoulder, has to have an adequately high flexural rigidity.
Since the flexural rigidity of the magazine is determined by the choice of material or rather the material's modulus of elasticity and the moment of inertia of an area, the dimensions, in particular the thickness of the magazine, determine the flexural rigidity of the magazine, which is a hole plate.
A pipetting device according to the invention is based on the aforementioned second sealing principle.
In all of the prior art pipetting devices of this type, a magazine, populated with pipette tips, is pushed, like a drawer, into a vertically moveable magazine holder, which represents a frame that is open on one side, as far as an end stop and then is pulled or pushed (drawer principle) against the sealing plate with a very powerful drive of the frame. The frame has lateral guide faces and an end stop, in order to put the magazine in a defined position inside the frame so that the pipette tips are assigned to the sleeves in such a way that they are in alignment.
The drawback with the drawer principle is that free space in front of the pipetting device is absolutely mandatory to ensure accessibility for pushing and pulling the magazine in and out.
In the event that the tips are to be changed automatically, an additional handling device for pushing and pulling the magazine in and out is necessary. Free access to the pipetting device is also absolutely mandatory for this device. If the tips are not changed by a lab robot with a relatively large working area, then it is also necessary to provide storage places for magazines with fresh pipette tips and for magazines with used pipette tips in the immediate vicinity of the pipetting devices. To date deck systems have not used the pipetting devices according to the aforementioned second sealing principle.
Deck systems are automatic pipetting systems, in which all of the sample carriers, the reagent reservoirs and aids, like pipette tips, which are necessary for processing a specific laboratory task, are disposed stationarily in a so-called deck position so that they are accessible to a pipetting device that can be moved in three axes in order to reach each deck position. Access for a pipetting device or a gripper is routinely from the top, for which reason such deck systems known from the prior art use only pipetting devices with pipette tips that are connected to the pipetting channels according to the cone principle.
A pipetting device according to the aforementioned second sealing type, which is also used for a pipetting device according to the invention, is known from the utility model specification DE 20 2008 013 533 U1.
The pipetting device includes as the essential components or rather modules a base plate comprising passage bores, a pump system with a plurality of pipetting channels, comprising a sleeve, which is fitted into the passage bores, an elastic sealing plate with holes and a magazine, populated with pipette tips. In this case the passage bores and consequently, fitted therein, the sleeves, the holes of the sealing plate and the pipette tips are arranged in an identical grid on a common mechanical axis. The magazine is connected by means of a gear mechanism to a drive motor.
The gear mechanism translates the rotary motion and the torque of the drive motor into a linear lifting motion and a tightening force acting on the magazine holder.
The result is that the pipette tips are lifted up to the sealing plate and, coaxially enclosing the sleeves, are pressed by means of their shoulder against the sealing plate with an adequately large tightening force, so that the pipette tips are sealed off from the sleeves.
The magazine and the magazine holder are designed according to the utility model specification DE 20 2008 013 533 U1 in such a way that the magazine can be inserted into the magazine holder like a drawer.
The major distinction between the other pipetting devices of this kind and the pipetting device according to the utility model specification DE 20 2008 013 533 U1 lies in the design of the tightening of the magazine. The rotary motion generated by a drive motor is translated by way of two identical eccentric gear mechanisms into a lifting motion of the magazine frame. In this case the eccentric gear mechanism is mounted on the base plate so as to be fixed relative to the frame. For this reason the housing of the pipetting device remains completely unaffected by the force transmission path when tightening the magazine.
The pipetting device, according to the utility model specification DE 20 2008 013 533 U1, has the same drawbacks as the above-described pipetting devices that were designed on the basis of the drawer principle.